For many applications, it is desirable to have available an aircraft which can take off from as small an area as possible and does not therefore require a special large-area airport. For specific purposes, moreover, an aircraft is required which is agile and can be manoeuvred in a precise manner and which can preferably hover on the spot and display good hovering properties.
For example, aircraft are used for air surveillance and reconnaissance which should to be able to hover over an interesting target and for example take aerial photographs. In an alternative application, a vertical take-off aircraft, sometimes also referred to as a VTOL (Vertical Take-off and Landing), can be used to fly to regions that are difficult to access for humans or for other machines, for example in the context of civil protection interventions, in order for example to transport goods such as tools, foodstuffs and drugs in such regions.
For such interventions, there have been developed, amongst others, aircraft in which four or more propellers or rotors equipped with a propeller and at least one drive motor provide for an essentially vertically upward thrust so that the aircraft can thus rise vertically or hover. An aircraft provided with four such rotors is also referred to as a quadcopter, quadrocopter, quadricopter, quadrotor or hover platform. Such aircraft with more than three rotors providing the lift are generally referred to as multicopters, wherein, apart from quadcopters, variants with three rotors (tricopters), six rotors (hexacopters) or eight rotors (octocopters) are commonplace. Such aircraft are usually operated unmanned and can be correspondingly small. In some cases, these aircraft are also referred to as drones.
By a slight inclination of the overall aircraft or one or more rotors out of the horizontal, it is possible in the case of such aircraft also to provide a certain propulsion, in that a thrust generated by the rotors is inclined out of the vertical. In the case if quadrocopters and multicopters when operated with electric motors, the inclination is often regulated by a rotation speed control of the electric motors. That is to say that the flight controller of the craft controls the thrusts of the individual propellers through their respective rotational speed. The individual thrusts can thus be manipulated in such a way that the aircraft can rise or fall, or can be inclined forwards, backwards or laterally. As a result of these targeted rotational speed changes, however, not only the thrusts are changed, but also the torques or angular momentum from the motors, and the propellers. A torque thus arises around the vertical axis of the system. This torque can act in the clockwise direction or anticlockwise direction. A control of the aircraft's rotation around the vertical axis of the aircraft is thus possible. Such electrically driven multicopters make use of the change in the torque or angular momentum without blade adjustment.
However, such aircraft have the drawback that with an increasing size of the aircraft it becomes more difficult to change the angular momentum sufficiently.